Based on the definition of logarithms, what is the difference in hydrogen ion concentration between a substance with a pH of 2 and a substance with a pH of 3?

The pH scale is logarithmic: each decrease of 1 pH unit means the hydrogen ion concentration is 10 times greater. Since pH 2 is one unit lower than pH 3, the pH 2 substance has 10 times the H+ concentration. Therefore, choice A is correct; a 100-fold difference would require a two-unit pH difference.

AI-written and checked against the verified answer.